Tiziano Rimoldi

Porphyrin conjugated SiC/SiOx nanowires for X-ray-excited photodynamic therapy

The development of innovative nanosystems opens new perspectives for multidisciplinary applications at the frontier between materials science and nanomedicine. Here we present a novel hybrid nanosystem based on cytocompatible inorganic SiC/SiOx core/shell nanowires conjugated via click-chemistry procedures with an organic photosensitizer, a tetracarboxyphenyl porphyrin derivative. We show that this nanosystem is an efficient source of singlet oxygen for cell oxidative stress when irradiated with 6 MV X-Rays at low doses (0.4–2 Gy). The in-vitro clonogenic survival assay on lung adenocarcinoma cells shows that 12 days after irradiation at a dose of 2 Gy, the cell population is reduced by about 75% with respect to control cells. These results demonstrate that our approach is very efficient to enhance radiation therapy effects for cancer treatments.

2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces.

We investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For this, we combine micro-tracking in real-space with measurement in momentum-space via x-ray photon-correlation spectroscopy and Digital Fourier Microscopy. Using these complementary techniques, we extend the spatial range of investigation beyond the limits of each one. We find a dynamical transition from Brownian diffusion to an arrested state driven by compression, characterized by intermittent rearrangements, compatible with a repulsive glass phase. The rearrangement and relaxation of the monolayer structure results dramatically hindered by the presence of NPs, which is relevant to explain some the mechanical features observed for the dynamic surface pressure response of these systems and which can be relevant for the respiratory physiology and for future drug-delivery composite systems.

Hydrophobic Silica Nanoparticles Induce Gel Phases in Phospholipid Monolayers

Silica nanoparticles (SiNP) can be incorporated in phospholipid layers to form hybrid organic-inorganic bidimensional mesostructures. Controlling the dynamics in these mesostructures paves the way to high-performance drug-delivery systems. Depending on the different hydrophobicity/hydrophilicity of SiNP, recent X-ray reflectivity experiments have demonstrated opposite structural effects. While these are reasonably well understood, less is known about the effects on the dynamics, which in turn determine molecular diffusivity and the possibility of drug release. In this work we characterize the dynamics of a mixed Langmuir layer made of phospholipid and hydrophobic SiNP. We combine X-ray photon correlation spectroscopy and epifluorescence discrete Fourier microscopy to cover more than 2 decades of Q-range (0.3-80 μm(-1)). We obtain evidence for the onset of an arrested state characterized by intermittent stress-relaxation rearrangement events, corresponding to a gel dominated by attractive interactions. We compare this with our previous results from phospholipid/hydrophilic SiNP films, which show an arrested glassy phase of repulsive disks.

CeF3-ZnO scintillating nanocomposite for self-lighted photodynamic therapy of cancer

We report on the synthesis and characterization of a composite nanostructure based on the coupling of cerium fluoride (CeF3) and zinc oxide (ZnO) for applications in self-lighted photodynamic therapy. Self-lighted photodynamic therapy is a novel approach for the treatment of deep cancers by low doses of X-rays. CeF3 is an efficient scintillator: when illuminated by X-rays it emits UV light by fluorescence at 325 nm. In this work, we simulate this effect by exciting directly CeF3 fluorescence by UV radiation. ZnO is photo-activated in cascade, to produce reactive oxygen species. This effect was recently demonstrated in a physical mixture of distinct nanoparticles of CeF3 and ZnO [Radiat. Meas. (2013) 59:139–143]. Oxide surface provides a platform for rational functionalization, e.g., by targeting molecules for specific tumors. Our composite nanostructure is stable in aqueous media with excellent optical coupling between the two components; we characterize its uptake and its good cell viability, with very low intrinsic cytotoxicity in dark.

Effect of a halogen-based precursor on dopant incorporation in 3C-SiC film epitaxy

Silicon carbide thin films were synthesised by vapour phase epitaxy technique on silicon substrates using silane and propane as precursors. Methyltrichlorosilane (MTS) was added, and nitrogen was used as dopant precursor. Samples with different doping concentrations were obtained varying the nitrogen flow during the growth. Doping level for each sample was assessed using Raman technique, and a correlation between dopant flow and doping level was confirmed. The influence of MTS on nitrogen incorporation is analysed and discussed: the introduction of MTS increases the growth rate and increases the doping level. We exclude a direct doping effect by the MTS, but we think that it promotes the incorporation of nitrogen doping species. The crystalline quality of the as-grown films was evaluated using X-ray diffraction, assessing the good crystalline quality even in samples obtained using high growth rates and high doping level.

Fracture Surface Characterisation of Friction Stir Processed Magnesium Alloy after Mechanical Tests

A high pressure die cast Mg-9%Al-1%Zn alloy was friction stir processed at two high rotation rates and advancing speeds. Tensile tests were performed at higher temperature to study the mechanical properties of the microstructure induced by the friction stir process. Fracture surfaces resulting from tensile tests were observed by scanning electron microscopy and investigated by microanalysis. The fracture occurred in the tmaz and inside the stirring zone, depending on deformation conditions (temperature and strain rate). The morphology of the fracture surface varied from ductile to brittle in the same sample depending on phase type. Microhardness was measured on cross sections perpendicular to the advancing direction of the stirring pin, at various depth levels, before performing tensile tests to estimate the attitude of a single region to be deformed.

Buffer Layer Optimization for the Growth of State of the Art 3C-SiC/Si

We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-SiC on (001) Si substrates. A 100 – 150 nm thick SiC buffer was deposited after a standard carbonization at 1125 °C, while increasing the temperature from 1125 °C to 1380 °C. Ramp time influenced the quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface. After the optimization of the buffer, to demonstrate its effectiveness, a high-quality 3C-SiC was grown, with excellent surface morphology, crystallinity and low stress.